WO1994000360A1

WO1994000360A1 - Dual cam axial clamp

Info

Publication number: WO1994000360A1
Application number: PCT/US1992/005209
Authority: WO
Inventors: Paul S. Petersen
Original assignee: Rosemount Inc.
Priority date: 1992-06-19
Filing date: 1992-06-19
Publication date: 1994-01-06

Abstract

A dual cam operated clamp (10) having a housing (11) which changes its effective diameter due to the rotation of cam pins (29, 30) having a linking member (40) which holds the cam pins (29, 30) in place and provides a spring force to clamp the housing (11).

Description

DUAL CAM AXIAL CLAMP

BACKGROUND OF THE INVENTION

The present invention relates to an improvement in a clamp for an injection molding heater that simply and easily provides a clamping force to clamp a heater onto a cylindrical nozzle for heating the nozzle.

Nozzle heaters for injection molds are helically wound around the nozzles. The nozzles are recessed into cavities and access for tightening the heaters onto the nozzle is restricted. The ability to adjust the heater clamping force from the open end of the recess is desired, and this is accomplished in U.S. Patent 4,968,247. The clamp in U.S. Patent 4,968,247 has formed cylindrical journals around cam hubs, and a formed cam follower encompassing a cam center which requires much machine work and substantial manufacturing costs. The present invention utilizes dual cam members to achieve double clamping force having a linking member holding the cams in place, and eliminates substantial manufacturing costs by removing the cam follower and reducing the cylindrical journals to semi-cylindrical partial journals.

SUMMARY OF THE INVENTION The present invention relates to an improvement to a clamp for a heater used with injection nozzles, or other cylindrical objects or heaters, which utilizes a formed, generally cylindrical housing which has a slit or slot along a longitudinal line. A cam member is rotatably mounted on each side of the slit, the cam members being held in place by a linking member which links the cams using an offset center portion of the cam members. The linking member has partial journals formed at opposite ends thereof which engage the center portions of the respective cam members. Rotation of a single cam member urges the opposing edges of the housing slit together, thereby tightening the clamp onto the heater. Rotation of both cam members results in twice the tightening motion. Thus the use of two cams doubles the range of tightening movement available over previous one cam systems. The linking member acts as a spring element to absorb changes in size of the heater caused by thermal changes so the clamp does not lose its clamping force.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side elevational view of a heater clamp housing made according to the present invention shown in place on an injection nozzle, with parts in section and parts broken away;

Figure 2 is a flat layout of the clamp housing before forming it into its clamp shape;

Figure 3 is a top plan view of the heater clamp housing;

Figure 4 is a side elevational view of a heater clamp housing;

Figure 5 is an end elevational view of the present invention; Figure 6 is a sectional view taken along lines

6—6 in Figure 4 with the cam center portions in an outer position; and

Figure 7 is a side elevational view of a cam pin. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A heater clamp indicated generally at 10 includes a clamp housing 11, which surrounds a heater element 12. The heater element 12 is a helically wound heater of the type well known and is described in more detail in U.S. Patent 4,968,247.

The housing 11 is formed from a flat sheet, as seen in Figure 2, and is formed with notches cut out to leave tabs 20,20 and 22,22 at ends 21 and 23, respectively. When housing 11 is made, the main portion is formed into a substantially cylindrical shape while leaving a slit 16 between the edges of the housing, as seen in Figure 3. The tabs 20,20 and 22,22 are curved oppositely and outwardly from the substantially cylindrical housing 11 to form semi-cylindrical partial journals 24 and 26, respectively, for cam pins or members 29 and 30, respectively. The partial journals 24 and 26 are clearly shown in Figure 5. The cam pins 29 and 30 are substantially identical. By way of example, the cam pin 30, as is seen in Figure 7, has hub ends 32 and 34 that are of a size to fit into the partial journals 24 and 26 formed by the tabs 20 and 22 and rotate therein. A cam center portion 36 is connected between hubs 32 and 34, and is formed by making a recess between hubs 32 and 34 and leaving a central axis of rotation 37. An axis 33 of the hubs 32 and 34 is offset from the axis of rotation 37 of center portion 36. A linking member 40 provides a restraining force to maintain hub ends 32 and 34 against partial journals 24 and 26 and hold the cam pins 29 and 30 in place. The linking member- 40 limits or controls the spacing or distance between the central axes 37 of rotation of cam pins 29 and 30 so that clamping forces can be developed with rotation of eccentric hubs 32 and 34. The linking member 40 has a longitudinal length substantially equal to that of the axial length of the cam center portions 36, as is shown in Figure 4. The linking member 40 has opposite ends that are curved to form semi-cylindrical partial journals 42 and 44 at opposite ends thereof which fit over a portion of the cam center portions 36 of cam pins 29 and 30. In the preferred embodiment, the cam pins 29 and 30 are maintained in the partial journals 24 and 26, and, 42 and 44 due to the opposed spring forces of the linking member 40, and the housing 11. The cam pins 29 and 30 rotate inside the partial journals 42 and 44, and, 24 and 26.

In operation, with the clamp housing 11 surrounding a heater element 12 as seen in Figure 1, a suitable tool or wrench 31 is inserted into a drive recess 35 in the end of either hub 32 or 34. By turning the wrench 31, each cam pin 29 and 30 can be rotated. Rotating cam pin 30 causes the cam hubs 32 and 34 to rotate around and change their effective radial position relative to the axis of rotation 37. The axis of rotation 37 of each cam pin is held substantially in place because the spring forces of the linking member 40 are greater then the spring forces of the housing 11, causing the hubs 32 and 34 to rotate about the center portion 36. When the cam pins 29 and 30 are rotated so that the corresponding axes 33 of hubs 32 and 34 are positioned inward of the corresponding central axis of rotation 37, as seen in Figure 6, the width of slot 16 and thus the diameter of housing 11 is decreased thus tightening the housing 11 with respect to the heater element 12. Because the spring force of linking member 40 is stronger, or more rigid, than the spring force of housing 11, the member 40 reacts against the cam center portions 36 causing the partial journals 24 and 26 to move the clamp housing inward thus decreasing the width of slot 16. In contrast, rotation of the cam pins 29 and 30 to position the hub axes 33 further apart will loosen the clamp housing 11. Minimum clamping forces are obtained when the axes 33 are farthest apart as shown in Figure 5. Although rotation of one cam pin will cause housing 11 to tighten, by using two cam pins 29 and 30, the clamping motion developed is approximately doubled over the clamping motion obtained from a single cam assembly.

The cam pin 30 may also contain marks 41,41 on the hubs 32 and 34 to indicate a maximum tightening or clamping position. When the marks 41,41 are at a minimum distance f om each other, as seen in Figure 5, the housing is in a loosened position. When the marks 41,41 are at a maximum distance from each other, the housing is in a maximum tightening position as shown in Figure 6.

The dual cam design of the present invention may also be used in a clamp housing having cylindrical journal straps that fully encompass the hubs, but by using the linking member 40 of the present invention, costly manufacturing time is eliminated. In previous clamp housings, such as U.S. Patent 4,968,247, full cylindrical journals are formed out of the housing. This design requires fine machining to form the journals and weld the journals in place. Using the linking member 40 of the present invention allows partial journals to be used, which requires much less machining and no welding, which eases manufacturing and is a big cost savings.

The linking member acts as a spring to maintain clamping force and absorb changes in size of the heater due to expansion and contraction of the heater from thermal effects.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A dual cam operated clamp comprising: a clamp housing for substantially surrounding and engaging a member to be clamped, the clamp having opposed adjacent edges whereby the clamp housing is tightened upon the member by urging the adjacent edges together; a plurality of rotatable cam members; and cam mounting means for rotatably mounting each rotatable cam member adjacent the housing, wherein each of the rotatable cam members has a rotational axis and a cam portion engaging the clamp housing, the cam portion changing its effective position relative to the rotational axis to urge an edge toward the other edge when the cam member is rotated, at least one cam member being provided for each edge.

2. The clamp as specified in claim 1 wherein the cam mounting means includes a linking member, the linking member engaging a cam member corresponding to each edge and controlling the distance between corresponding rotational axes.

3. The clamp as specified in claim 2 wherein the linking member engages each cam member with semi- cylindrical partial journals.

4. The clamp as specified in claim 1 wherein the clamp housing engages each cam member with semi- cylindrical partial journals.

5. The clamp as specified in claim 2 wherein each cam member includes two axially spaced end hubs substantially aligned on a longitudinal hub axis, the hubs connected together with a central shaft portion substantially on the rotational axis, wherein the longitudinal hub axis is radially offset from the rotational axis.

6. The clamp as specified in claim 5 wherein the linking member engages the central shaft portion of each cam member.

7. The clamp as specified in claim 1 wherein the clamp housing is substantially cylindrical.

8. The clamp as specified in claim 1 wherein the linking member comprises a spring to compensate for changes in heater size due to thermal changes.

9. A dual cam operated clamp comprising: a clamp housing for substantially surrounding a member to be clamped and having a slit to form first and second edges, the clamp housing tightenable upon the member by urging the first and second edges together; a first rotatable cam member; a second rotatable cam member; first journal means connected to the housing adjacent the first edge for rotatably supporting the first rotatable cam member; second journal means connected to the housing adjacent the second edge for rotatably supporting the second rotatable cam member; wherein each of the cam members comprises cam hubs connected together with a smaller central shaft portion having a central axis, an axis of the cam hubs being offset from the central axis, the cam hubs changing their effective position relative to the central axis of the central portion to urge an edge toward the other edge when the corresponding cam member is rotated; and a linking member connected between the first and second cam members to control the spacing between the central axes of the central portions.

10. The clamp as specified in claim 8 wherein the first and second journal means comprise semi-cylindrical partial journals formed along each corresponding edge, the semi-cylindrical partial journals of the first journal means engaging the cam hubs of the first rotatable cam member, the semi-cylindrical partial journals of the second journal means engaging the cam hubs of the second rotatable cam member. -lu¬

11. The clamp as specified in claim 9 wherein the linking member engages the central shaft portion of each rotatable cam member.

12. The clamp as specified in claim 10 wherein the linking member engages each cam member with semi- cylindrical partial journals.