Apparatus and method for the linear movement of a shaft

Abstract

An apparatus and a method for linear movement of a shaft are described, in particular of a hydraulic press, comprising at least one piston controlled by means of at least one first and one second proportional valve, wherein the piston defines a piston chamber and a rod chamber and wherein each proportional valve is provided with respective first and second chambers for containing a fluid. At least one of the at least two proportional valves is connected to the piston, so as to make the fluid contained both in the respective first chamber and in the respective second chamber flow into the piston chamber of the aforesaid piston.

Description

[0001] APPARATUS AND METHOD FOR THE LINEAR MOVEMENT OF A SHAFT

[0002] DESCRIPTION

[0003] Field of the invention

[0004] The present invention concerns the field of hydraulic apparatuses for linear movement , in particular of an inj ection shaft of a piston .

[0005] State of the art

[0006] In the field of industrial automation, the use of inj ection molding machines , in particular for inj ecting polymers such as plastics and similar materials , is well known . Such pres ses provide for the use of one or more pistons hydraulically controlled by means of proportional valves for controlling the various steps of a respective plastici zing screw inj ecting a molten plastic mass into the cavity of a mold .

[0007] The hydraulically controlled pi ston, or hydraulic piston, is generally of the double-acting type and defines a piston chamber, for carrying out the forward movement of the piston rod in the inj ecting step, and a rod chamber, for the step of sucking in or retracting the piston .

[0008] In recent years , with the increasing costs of raw materials , with the arrival of a tax to discourage the use of plastic products - named plasti c tax - and to reduce the environmental impact of plastic items , the possibility to reduce the weight of plastic manufactured products by reducing their thickness is increasingly required . In order to produce items with increasingly thinner walls , it is necessary to inj ect the molten polymer mass into the cavity of the mold in the shortest possible amount of time , so as to prevent it from cooling and therefore solidi fying against the wall s of the mold before the mold has been filled, or anyhow before the product is finished .

[0009] In an attempt to overcome this problem, various solutions providing for the use of two proportional valves connected in parallel and acting on the same piston for doubling its speed, have been suggested .

[0010] In order to further decrease the thicknesses of the products , it would be necessary to be able to further increase the inj ection speed . For example , it would be desirable to be able to triple the speed, but this would involve the use of three proportional valves , with a signi ficant increase in costs and the space necessary for housing them .

[0011] Object and summary of the invention

[0012] Obj ect of the present invention is to provide an apparatus for the linear movement of a shaft , in particular of a press , which is simultaneously simple to make , compact and able to increase the movement speed compared with the devices of the known art .

[0013] A further obj ect is to suggest an apparatus which allows to increase the movement speed without increasing costs and volumes compared with the known art .

[0014] A further obj ect of the present invention is to provide a method for the linear movement of a shaft , in particular of a press , which allows to increase the movement speed compared with the known art .

[0015] In other words , the present invention aims to provide an apparatus and a method which allow for improved performance , in particular in terms of speed, with the same volumes and costs , compared to what is already on the market .

[0016] The present invention therefore concerns an apparatus according to claim 1 .

[0017] In particular, the present invention concerns an apparatus for the linear movement of a shaft , in particular of a press , which comprises at least one piston with which at least two respective inj ection valves , preferably of the proportional type , are combined for moving the piston rod so as to inj ect a molten material , in particular a plastic material , into a mold, wherein at least one first valve performs the inj ecting and sucking in and discharging steps , and at least one second valve is connected so that both its inj ecting and sucking in and discharging passages are intended for inj ection .

[0018] Advantageously, the at least two inj ection valves are of the double-acting type .

[0019] Actually, the Applicant noticed that greater pressure is required for inj ecting the molten material into the cavity of the mold, than the pressure necessary for bringing the pi ston rod back to its initial position . Consequently, the amount of fluid, generally oil , to be discharged during inj ection is therefore much less than the one to be inj ected for carrying out the inj ecting step ; consequently, it is suf ficient for only one valve to carry out the sucking in and discharging step, allocating both the two inj ecting and sucking in and discharging stages of at least one second valve to inj ection .

[0020] This way, in the case of two valves connected according to the present invention for example , the two valves carry out three inj ecting and one sucking in and discharging steps instead of carrying out two inj ecting and two sucking in and discharging steps , thereby signi ficantly increasing ( from two to three times ) the inj ection speed, for the same number of valves ( two in the present case ) .

[0021] More in detail , the linear movement apparatus comprises at least one piston defining a piston chamber and a rod chamber, wherein the piston is controlled by means of at least two respective proportional valves , each provided with a respective first chamber and a respective second chamber for containing a fluid, and wherein at least one proportional valve is connected to the respective piston so as to make the fluid contained in both the respective first and second chambers flow into the piston chamber .

[0022] Advantageously, the at least two valves are connected parallel to one another .

[0023] At least the other of the at least two proportional valves is preferably connected to the respective piston so as to make the fluid contained in the respective first chamber flow into the piston chamber and the fluid contained in the respective second chamber flow into the rod chamber .

[0024] Advantageously, the piston is of the double-acting type , movable in two opposite directions .

[0025] Each of the at least two proportional valves is preferably provided with a supply connection and a discharge connection, and at least one of the two proportional valves is connected to the piston so that the supply connection and the discharge connection are both connected to the piston chamber . In a preferred solution, the discharge connection is connected to the piston chamber by means of a respective additional supply line .

[0026] In an even more preferred solution, the additional supply line is in fluid connection with a supply line of the valve itsel f , which valve is in turn in fluid connection with the piston chamber .

[0027] Advantageously, at least the other of the at least two proportional valves is connected to the respective piston so that the supply connection is connected to the piston chamber and the discharge connection is connected to the rod chamber .

[0028] In an alternative embodiment, the flow of the fluid can be reverted so that the flow of the fluid is directed from the discharge connection towards the supply connection in at least one or both or all the valves . In this case , the supply connection of at least one of the two valves is connected to the piston chamber by means of a respective additional supply line . Also in this case , the additional supply line can be in fluid connection with a supply line of the valve itsel f , which valve is in turn in fluid connection with the piston chamber .

[0029] Advantageously, i f a piston is connected and driven by more than two proportional valves , the number of valves to be intended for inj ecting and sucking in and discharging and that of the valves to be intended for inj ection only, by means of both its chambers , is established depending on the volume , and in particular depending on the ratio of the volumes of the piston chamber and the rod chamber of the respective piston . The movement apparatus is preferably intended for the linear movement of a shaft of a hydraulic press .

[0030] The invention also concerns a hydraulic press comprising a l inear movement apparatus of the type described above .

[0031] Advantageously, the hydraulic press comprises at least one plastici zing unit with which a respective piston of the movement apparatus is combined, to cause the movement of the piston so as to perform the inj ection of a mass of molten material , in particular of a plastic material , into a mold .

[0032] The invention also concerns a method according to claim 11 , for using an apparatus for the linear movement of a shaft and comprising at least one piston, comprising a piston chamber and a rod chamber at least one first and one second proportional valve combined with the piston and each provided with a respective first chamber and a respective second chamber for containing a fluid, wherein the method provides for making the fluid contained both in the first and the second chambers of the at least one second proportional valve flow into the piston chamber .

[0033] This way, the flow rate of the fluid entering the piston chamber is signi ficantly increased by making the fluid of both chambers of at least one second proportional valve flow into the piston chamber, thereby increasing the inj ection speed .

[0034] Advantageously, the method further provides to make the fluid contained in the first chamber of the at least one first proportional valve flow into the piston chamber and

[0035] - the fluid contained in the respective second chamber flow into the rod chamber .

[0036] This allows at least one first valve supplying the piston chamber, thereby contributing to the inj ection of the material but also simultaneously supplying the rod chamber to bring back the rod of the piston to an initial backward position, so as to allow a subsequent inj ection to be performed .

[0037] Brief list of the figure

[0038] Further characteristics and advantages of the invention will become clearer in the review of the following detailed description of a preferred, although not exclusive , embodiment illustrated by way of example and without limitations with the aid of the accompanying drawing, in which the only figure is a schematic view of an apparatus for the linear movement of a shaft according to the present invention .

[0039] Detailed description of the invention

[0040] The figure shows an apparatus for the linear movement of a shaft , in particular of a hydraulic press .

[0041] As shown, the movement apparatus 1 comprises : at least one piston 2 , at least one first proportional valve 3 and at least one second proportional valve 4 .

[0042] The proportional valves 3, 4 are of the double-acting type .

[0043] A plastici zing unit 5 , comprising a respective plastici zing screw 6for inj ecting a mass of molten plastic material into a mold not shown, is combined with the piston .

[0044] The piston is of the hydraulically controlled type , also named hydraulic piston, and double-acting, i . e . provided with a rod 7 movable in two opposite directions .

[0045] The piston actually defines a piston chamber 8 for carrying out the forward movement of the piston rod 7 in the inj ecting step, and a rod chamber 9 for the step of sucking in or retracting the piston rod .

[0046] The forward and backward movements of the rod are controlled by means of the aforesaid inj ection valves .

[0047] According to the invention, each piston is hydraulically controlled by means of at least one first proportional valve 3 and at least one second proportional valve 4 , for controlling the various steps of the respective plastici zing screw 6, for inj ecting a mass of molten plastic material into the cavity of a mold .

[0048] The proportional valves each comprise a respective first connection Al , A2 and a respective second connection Bl , B2 . Usually, in the proportional valves , during the forward movement step, the first connection Al , A2 is connected to a respective supply connection Pl , P2 for supplying, via a respective supply line LI , L2 , a first fluid generally to the piston chamber 8 , so as to cause the rod to move forward, while the second connection Bl , B2 is connected to a respective discharge connection T1 , T2 , to discharge , via a discharge line LT, a second fluid from the rod chamber 9, thereby allowing the rod 7 to retract .

[0049] The at least one first and at least one second proportional valves are connected parallel to one another . Advantageously, the Applicant noticed that the piston chamber 8 , which manages the inj ection of the molten plastic mass into the cavity of the mold, has a volume signi ficantly greater than that of the rod chamber and has consequently designed a new mode o f connecting the at least two proportional valves which allows , with the same number of valves , the speed of the piston to be increased by at least 1 / 2 during the inj ecting step compared to the solutions according to the known art , consequently increasing the flow rate of plastic material towards the mold .

[0050] In other words , during the inj ecting step, i f in a system comprising two proportional valves according to the known art the flow rate can be equal to two times the flow rate of the single valve , in the system according to the invention, with the same two proportional valves , it is possible to achieve a flow rate equal to three times the flow rate of the individual valve . The increasing of the flow rate of molten material per unit of time corresponds to an increase in the inj ection speed, as per the obj ect of the present invention .

[0051] Such result is achieved by using : at least one first proportional valve 3, wherein the first and second connections Al , Bl are connected in a conventional way, so as to respectively make the fluid contained in a first chamber a' , in fluid communication with the supply connection Pl , flow into the piston chamber 8 , by means of a respective supply line LI and the fluid contained in a second chamber b' , in fluid communication with the discharge connection Tl , flow into the rod chamber 9, and at least one second valve 4 acting as a "booster" , making the fluid contained both in the respective first chamber a" and the respective second chamber b" flow into the piston chamber 8 , which manages the inj ection, thus increasing the flow rate thereof .

[0052] In other words , at least one first proportional valve is connected in a conventional way, with the first connection Al connected to the respective supply connection Pl to make the fluid flow into the piston chamber 8 , by means of the respective supply line LI , and with the second connection Bl connected to the respective discharge connection Tl , and connecting at least one second proportional valve with the first connection A2 in fluid connection with the respective supply connection P2 , to make the fluid flow into the piston chamber 8 , via the respective supply line L2, and the second connection B2 connected to the respective discharge connection T2 , with the discharge connection T2 connected, via a respective additional supply line LA, to the supply line L2 .

[0053] Alternatively, the additional supply line LA can be connected so as to directly converge into the piston chamber 8 .

[0054] Such solution therefore allows for a fluid flow rate in the inj ection piston chamber three times greater than the conventional solution with only one proportional valve and anyhow greater than the solution using two proportional valves connected in a conventional way . This allows the speed of the rod and consequently of the inj ection of molten material to be increased, thereby allowing items of reduced thickness to be made .

[0055] Actually, compared to a solution with two proportional valves , it allows for three supply lines instead of two , i . e . the supply lines of the first and second proportional valves and the additional supply line of the second proportional valve , which are highlighted with a stroked line in the figure . This way, only the second connection Bl of the first proportional valve is connected to the rod chamber 9, by means of a respective third line L3 highlighted in gray in the figure .

[0056] Such a solution can also be adopted with more than two proportional valves combined with a respective piston, by simply calculating how many valves are to be intended for the inj ecting and sucking in and discharging and how many valves can be intended for the inj ection only, depending on the volume , and in particular depending on the ratio of the volumes of the piston chamber and rod chamber of the at least one piston connected to the respective plastici zing screw .

[0057] Such a movement apparatus can be combined with a hydraulic press .

[0058] In particular, a respective plastici zing unit for inj ecting a mass of molten plastic material can be combined with each piston of the movement apparatus .

[0059] The method of using the movement apparatus substantially provides for making the fluid contained in the first and second chambers of at least one of the two proportional valves flow into the piston chamber . Additionally, the method provides for making the fluid contained in the first chamber of the other proportional valve flow into the piston chamber and for making the fluid contained in the second chamber of the aforesaid other valve flow into the rod chamber .

[0060] In summary, the present linear movement apparatus , in particular for hydraulic presses , is characteri zed by providing the possibility of combining at least two proportional valves of the double-acting type with each piston, the valves being connected to the respective piston so that one of them ( or at least one of them in case of three or more proportional valves ) is connected to the respective piston, so that both its chambers are connected to the piston chamber of the respective piston . In other words , both chambers of the aforesaid proportional valve , or at least one proportional valve , are intended for inj ection only .

[0061] In order to meet contingent and speci fic needs , a technician of the field can make numerous changes and modi fications to the present invention or embodiments shown and described, all thereby comprised in the protection scope of the invention as defined in the following claims .

Claims

CLAIMS1. A movement apparatus (1) for moving a shaft, comprising at least one piston (2) controlled by at least one first respective proportional valve (3) and at least one second respective proportional valve (4) that are combined therewith,- wherein said at least one piston defines a piston chamber (8) and a rod chamber (9) ,- wherein each of said at least one first proportional valve (3) and at least one second proportional valve (4) is provided with a respective first chamber (a' , a") and a respective second chamber (b' , b") for containing a fluid, the movement apparatus being characterized in that said at least one second proportional valve is connected to the respective piston so as to make the fluid contained both in the respective first chamber (a") and in the respective second chamber (b") flow into the piston chamber (8) of said piston.

2. Movement apparatus (1) according to claim 1, wherein said at least one first proportional valve (3) is connected to the respective piston so as to make the fluid contained in the respective first chamber (a' ) and the fluid contained in the respective second chamber (b' ) flow respectively into said piston chamber (8) and into said rod chamber ( 9 ) .

3. Movement apparatus (1) according to any one of claims 1 or 2, wherein each of said at least one first and one second proportional valve (3, 4) is provided with a supply connection (Pl, P2) and a discharge connection (Tl, T2) and wherein said at least one second proportional valveis connected to the respective piston so that the respective supply connection (P2) and the respective discharge connection (T2) are both in fluid connection with the piston chamber (8) .

4. Movement apparatus (1) according to claim 3, wherein said discharge connection (T2) is connected to said piston chamber (8) by means of a respective additional supply line (LA) .

5. Movement apparatus (1) according to claim 4, wherein said additional supply line (LA) of said at least one second proportional valve is fluidically connected to a supply line (L2) of said at least one second proportional valve (4) , which second proportional valve is in turn in fluid connection with said piston chamber (8) .

6. Movement apparatus (1) according to any one of the preceding claims, wherein said at least one first proportional valve is connected to the respective piston so that the respective supply connection (Pl) is in fluid connection with the piston chamber (8) and the respective discharge connection (Tl) is in fluid connection with the rod chamber (7) .

7. Movement apparatus (1) according to any one of the preceding claims, wherein said at least one piston is connected and driven by more than two respective proportional valves and wherein the number of proportional valves to be intended for the injecting and sucking in and discharging steps and that of the proportional valves to be intended for injection only are established depending on the volumes of the piston chamber (8) and the rod chamber (9) of said piston, preferably depending on the ratio ofthe aforesaid volumes.

8. Movement apparatus (1) according to any one of the preceding claims, intended for the linear movement of a shaft (1) for a hydraulic press.

9. Hydraulic press comprising a movement apparatus (1) according to any one of the preceding claims.

10. Hydraulic press according to claim 9, wherein a plasticizing unit (5) , for injecting a mass of molten plastic material, is combined with each piston (2) of said movement apparatus (1) .

11. Method of using a movement apparatus (1) for moving a shaft, wherein said movement apparatus comprises at least one piston (2) controlled by means of at least one first respective proportional valve (3) and at least one second respective proportional valve (4) that are combined therewith,- wherein said at least one piston defines a piston chamber (8) and a rod chamber (9) ,- wherein each of said at least one first proportional valve (3) and at least one second proportional valve (4) is provided with a respective first chamber (a' , a") and a respective second chamber (b' , b") for containing a fluid, the method being characterized by the step of making the fluid contained both in the first chamber (a") and the second chamber (b") of said at least one second proportional valve flow into the piston chamber (8) .

12. Method of using a movement apparatus (1) for moving a shaft according to claim 11, wherein the further step of- making the fluid contained in the first chamber (a' ) of said at least one first proportional valve (3) flow into said piston chamber (8) and the fluid contained in the respective second chamber (b' ) flow into said rod chamber ( 9 ) , is provided .

Images