The scoop? SLA-500 heat exchangers

From: DANIEL CHARLES DAVIS (DANIEL@proton.com.my)
Date: Fri Mar 12 1999 - 03:23:35 EET


All,

OK, I have dug further into this and what Eric is saying is true, to a
point. It seems that 3D buys LaserPure 20 and upgrades them to an
"LP40" at their manufacturing site. I was told (by 3D) that it is only
a valve change (no specifics indicated) and the unit shipped with the
SLA500 retains the "LaserPure 20" identification. There was no mention
of a heat exchanger upgrade (indeed our units, installed 7/97, have
model CB26-50H exchangers). The reason stated was that this method is
less costly than buying the LaserPure 40 outright.

What does this mean? I'm not sure, but Coherent's documentation specs
an LP40, which is significantly different in terms of flow rates &
cooling capacity, which points to a larger heat exchanger in the LP40,
not just a valve. The chart below shows only the specs that differ
between the two:

                            LP 20 LP 40
- Cooling capacity at maximum
  plant side flow rate 20 kW 40 kW

- Temperature delta at maximum
  plant side flow rate 4C 5C
                                 (39F) (41F)

- Plant water flow range 2-8 gpm 2.5-10 gpm
                                 (7.5-30 lpm) (9.5-38 lpm)

- Laser side flow (nominal) 2-3 gpm 5-7 gpm
                                 (7.5-11 lpm) (19-26.5 lpm)

- Laser side flow (maximum) 5 gpm 15 gpm
                                 (19 lpm) (57 lpm)
        Terms used in this table:
        Delta: The difference in water temperature between the
laser cooling loop
                                and the plant water source.
        Plant side: The side of the heat exchanger cooled by the
flow through water source.
        Laser side: The closed water loop that cools the laser

Interesting to me as we have been having condensation problems inside
the laser power supply. This is because the plant-water chillers have
been set at a low temperature to keep the lasers cool. We have been
told be 3D to increase both the temperature & flow of the plant water to
correct this problem. OK, no problem. The recommended flow rate is
35-40 litres/hour. If we do have the LP20 this cannot happen, as flow
is limited to 30 lpm max. Hmmm, problem. Also, if the LP40 heat
exchanger is larger, then maybe we can increase our plant water
temperature, still cool the laser, and things will be OK.

Should we install the LP40 heat exchangers (model CB26-90H)? We'll just
have to wait & see...

---
Regards,
Dan Davis
PROTON Rapid Prototyping & Manufacturing Center
Hicom Industrial Estate, Batu Tiga, PO Box 7100
Shah Alam, 40918 Selangor MALAYSIA
+60 3 515-2380 phone/fax
http://www.protoncar.com/rapid.htm

> > > -----Original Message----- > > > From: ERIC KING [SMTP:lzrdude@earthlink.net] > > > Sent: Monday, March 08, 1999 5:56 PM > > > To: rp-ml@bart.lpt.fi > > > Subject: SLA-500, heat exchangers > > > > > > Dear list, > > > > > > Please check your heat exchanger. > > > > > > It has come to our attention that there are several problems > > > concerning the Laser Pure heat exchangers on the SLA-500 machines: > > > > > > 1) The Coherent "Laser Pure 20" heat exchangers out in the field, > > > are not the correct model, and may cause severe damage to your > > > laser. They were not intended to be used with this model laser, > > > and we can supply detailed literature upon your request. > > > > > > 2) We have also seen "Laser Pure 40" models with the wrong > > > internal components. Which also may cause laser problems. > > > > > > To check for the correct component, remove the top lid, > > > and remove the side panel from the LP-40 unit. > > > (the side that has all the water fittings) > > > Locate the stainless steel heat transfer unit. > > > The unit should have the model # CB26-90H, > > > if it does not, please contact us. > > > > > > We have only seen these problems, on systems with dates prior to > > > 1992. > > > > > > If you have questions, or need more info, please contact us: > > > > > > Laser Innovations > > > (805) 529-5864 tel > > > 6621 fax > > > sla-500@laserinnovations.com > > > > > > Best regards, > > > > > > Eric King > > > > > > For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/ > > Gary, > > I apologize for my late reply, I've been out sick. > > Yes, you should replace the bypass with the 2.5 GPM. That is one of > the upgrades / modifications to convert an LP-20 to a 40. > > What is the model # on the heat exchanger, itself ? > > Best regards, > > Eric King > > For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/

For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/



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